Intermolecular 1,2-difunctionalization of alkenes

Alkenes are an important class of organic compounds with a carbon–carbon double bond and a wide range of industrial and natural sources. The presence of π bonds provides the possibility for many forms of transformations. The direct difunctionalization of olefins can continuously introduce two identical or different groups into the olefin molecule at one time, while achieving a rapid increase in molecular complexity, and it also gives the organic compound potential or specific application value. In general, olefin difunctionalization can be achieved via three different reaction modes. Firstly, metal species can add double bonds by employing transition metals; further coupling can then be followed to complete the difunctionalization. Another intriguing approach is that radicals add to the olefins and then are quenched in diverse ways. The ability to continuously introduce diverse functional groups is the most significant feature of this platform. The third mode is that the olefin is transformed into a cationic radical or anionic radical intermediate through single-electron transfer. This strategy is less developed and more novel, but has certain limitations. Driven by the innovation of synthetic chemistry strategies, the difunctionalization of olefins, which was previously difficult to achieve, has also been gradually achieved. This review updates the latest progress in the 1,2-difunctionalization of olefins in the past five years. We aim to classify reaction mechanisms and functional group types. It should be stated that reactions with olefin double bonds to form rings are not included here.